`What is intelligence?' may seem like a simple question to answer, but the study and measurement of human intelligence is one of the most controversial subjects in psychology. For much of its history, the focus has been on differences between people, on what it means for one person to be more intelligent than another, and how such differences might have arisen, obscuring efforts to understand the general nature of intelligence. These are obviously fundamental questions, still widely debated and misunderstood. New definitions of intelligence and new factors affecting intelligence are frequently being described, while psychometric testing is applied in most large industries. IQ and Human Intelligence provides a clear, authoritative overview of the main issues surrounding this fascinating area, including the modern development of IQ tests, the heritability of intelligence, theories of intelligence, environmental effects on IQ, factor analysis, relationship of cognitive psychology to measuring IQ, and intelligence in the social context. The clear, accessible style and numerous explanatory boxes make this the ideal text for advanced undergraduate and graduate students in psychology.